Aptamers, which are nucleic acid ligands capable of binding to molecular targets, have recently attracted increased attention for their potential application in many areas of biology and biotechnology. They may be used as sensors, therapeutic tools, to regulate cellular processes, as well as to guide drugs to their specific cellular target(s). Contrary to the actual genetic material, their specificity and characteristics are not directly determined by their primary sequence, but instead by their secondary and/or tertiary structure. Aptamers have been recently investigated as immobilized capture elements in a microarray format. Others have recently selected aptamers against whole cells and complex biological mixtures. Aptamers are typically characterized by binding to their target molecules via non-Watson-Crick (i.e. non-hybridization) mechanisms, such as by intermolecular forces resulting from the secondary or tertiary structure of the aptamer. This is especially true of non-nucleic acid target molecules where Watson-Crick mechanisms typically do not apply.
Aptamers are commonly identified by an in vitro method of selection sometimes referred to as Systematic Evolution of Ligands by EXponential enrichment or “SELEX”. SELEX typically begins with a very large pool of randomized polynucleotides which is generally narrowed to one aptamer ligand per molecular target. Once multiple rounds (typically 10-15) of SELEX are completed, the nucleic acid sequences are identified by conventional cloning and sequencing. Aptamers have most famously been developed as ligands to important proteins, rivaling antibodies in both affinity and specificity, and the first aptamer-based therapeutics are now emerging. More recently, however, aptamers have been also developed to bind small organic molecules and cellular toxins, viruses, and even targets as small as heavy metal ions.
Tetrahydrocannabinol (THC, dronabinol by INN), or more precisely its main isomer (−)-trans-Δ9-tetrahydrocannabinol (THC-delta 9), is the principal psychoactive constituent (or cannabinoid) of cannabis. It can be an amber or gold colored glassy solid when cold, which becomes viscous and sticky if warmed.
Like most pharmacologically-active secondary metabolites of plants, THC in Cannabis is assumed to be involved in self-defense, perhaps against herbivores. THC also possesses high UV-B (280-315 nm) absorption properties, which, it has been speculated, could protect the plant from harmful UV radiation exposure.
Dronabinol is the INN for a pure isomer of THC, (−)-trans-Δ9-tetrahydrocannabinol, which is the main isomer found in cannabis. It is used to treat anorexia in people with HIV/AIDS as well as for refractory nausea and vomiting in people undergoing chemotherapy. It is safe and effective for these uses.
THC is also an active ingredient in nabiximols, a specific extract of Cannabis that was approved as a botanical drug in the United Kingdom in 2010 as a mouth spray for people with multiple sclerosis to alleviate neuropathic pain, spasticity, overactive bladder, and other symptoms.